The invention relates to cutting elements for rotary drill bits for use in drilling or coring deep holes in subsurface formations.
Rotary drill bits of the kind to which the present invention is applicable comprise a bit body having a shank for connection to a drill string and an inner channel for suplying drilling fluid to the face of the bit. The bit body carries a plurality of so-called `preform` cutting elements. Each cutting element may be mounted directly on the bit body or on a carrier, such as a stud or post, which is received in a socket in the bit body. One common form of perform cutting element comprises a tablet having a hard facing layer of polycrystalline diamond or other superhard material and a backing layer formed of cemented tungsten carbide. The two-layer arrangement of the cutting element provides a degree of self sharpening since, in use, the less hard backing layer wears away more easily than the harder cutting layer. Another form of cutting element comprises a single unitary tablet of thermally stable polycrystalline diamond material.
The perform cutting elements, which are formed under massive pressure in a press, are most often in the form of circular discs and are mounted on the drill bit so that, in use, each element wears away along one portion of its peripheral edge. However, other configurations of cutting element are known, for example sectorshaped, equare and triangular elements, where the cutting action is performed by a projecting angular portion of the cutting element.
Conventional cutting elements of the kind described may not, however, provide the best cutting effect on certain types of formation being drilled, and the present invention sets out to provide an improved form of cutting element which is straightforward to manufacture and which may give more rapid drilling with some types of formation.